The technology used in modern energy saving lighting devices uses mercury as one of the active components. As mercury harms the environment, extensive research is done to overcome the complicated technical difficulties associated with energy saving, mercury-free lighting. Today, LED has emerged strongly, however this technology is made in very advanced semiconductor factories (“FAB”s) utilizing very costly equipment. In addition the LED technology today is struggling to achieve commercially attractive solutions for the deep UV (UVC) region as some fundamental physical issues are impeding the development.
An approach used for solving this problem is by using field emission light source technology. Field emission is a phenomenon which occurs when a very high electric field is applied to the surface of a conducting material. This field will give electrons enough energy such that the electrons are emitted (into vacuum) from the material.
In prior art devices, a cathode is arranged in an evacuated chamber, having for example glass walls, wherein the chamber on its inside is coated with an electrically conductive anode layer. Furthermore, a light emitting layer is deposited on the anode. When a high enough potential difference is applied between the cathode and the anode thereby creating high enough electrical field strength, electrons are emitted from the cathode and accelerated towards the anode. As the electrons strike the light emitting layer, typically comprising a light powder, the light powder will emit photons. This process is referred to as cathodoluminescence.
One example of a light source applying field emission light source technology is disclosed in EP1709665. EP1709665 disclose a bulb shaped light source comprising a centrally arranged field emission cathode, further comprising an anode layer arranged on an inside surface of a glass bulb enclosing the field emission cathode. The disclosed field emission light source allows for omnidirectional emission of light, for example useful in relation to a retrofit light source implementation.
Even though the EP1709665 shows a promising approach to a mercury free light source, it would be desirable to provide an alternative to the disclosed bulb structure, possibly allowing for enhanced manufacturing and thus reduced cost for the resulting light source. In addition, the manufacturing of a three-dimensional field emission light source as is shown in EP1709665 is typically someway cumbersome, specifically for achieving a high level of uniformity in regards to light emission.
“Field-emission light sources for lab-on-a-chip microdevices” by A. Górecka-Drzazga et. al., Bulletin of the polish academy of sciences technical sciences, Vol. 60, No. 1, 2012, disclose an interesting approach for overcoming the problems described. Specifically, there is disclosed a field emission chip comprising a nanostructured cathode.
Further attention is drawn to US20110297846, disclosing methods and devices for producing light by injecting electrons from field emission cathode across a gap into nanostructured semiconductor materials, electrons issue from a separate field emitter cathode and are accelerated by a voltage across a gap towards the surface of the nanostructured material that forms part of the anode.
However, the disclosed microdevices are not suitable as commercially viable light sources, that is, a lighting scenario not limited to short illumination cycles as would be the case of in relation to the above reference. There is thus a desire to provide further enhancements to a field emission light source, typically adapted for general purpose lighting and deep UV (UVC) light sources.